1. Field of the Invention
The present invention relates to a descaling nozzle for eliminating scale formed on a surface of a rolled steel plate through a linear jetting operation of highly-pressurized fluid (e.g. water) onto the surface, and more particularly to a descaling nozzle comprising a straightening passage including a straightener, a constricted passage communicating with downstream of the straightening passage and a jetting passage having a jetting opening at a bottom of a groove defined at a top end face thereof in the direction of diameter of the same with axes of the straightening, constricted and jetting passages being aligned on the same straight line.
2. Description of Prior Art
There is a known descaling nozzle of the above-described type as disclosed, for example, in a Japanese patent application published under SHOWA No. 43-23197. According to this conventional descaling nozzle, of the above constricted passage, an upstream passage portion has the same radius throughout its overall length and at the same time a downstream passage portion has a radius tapering towards the downstream side.
However, in the case of this descaling nozzle, although the straightening passage and the upstream passage portion of the constricted passage have the same radius each other, the straightening passage, as incorporating the straightener, has an actual passage section smaller than that of the upstream passage portion and the passage section area varies suddenly between the straightening passage and the constricted passage. As the result, although the fluid is once straightened through the straightening passage, the fluid is again disturbed with a vortex flow when entering the constricted passage. Therefore, in spite of the straightening passage, the fluid enters the jetting passage often in the form of the vortex flow again and the linearly-jetted fluid also becomes disturbed with its thickness becoming unnecessarily large. Consequently, these result in decrease or unevenness in collisional force of the jetted fluid and in deterioration of descaling efficiency of the nozzle.
Also, though not relating to a descaling nozzle, there is another known nozzle disclosed in a Japanese utility model application published under SHOWA No. 39-17657. In the case of this nozzle, the straightening passage and the constricted passage are formed as one continuous passage having a radius gradually decreasing towards its downstream side. It is conceivable that this art may be employed for forming a descaling nozzle. In this case, since the area of the passage section of the constricted passage becomes gradually reduced towards the downstream side and the same finally becomes equal to that of the downstream portion of the straightening passage at a position adjacent the upstream straightening passage, it is possible to prevent the generation of vortex flow at the time of the entrance of the fluid from the straightening passage into the constricted passage. However, since the straightening passage also has its radius gradually reduced towards the downstream side, there occur problems to be described next.
In the case of the above-described construction, the following arrangement is required of the straightener. That is, an outer periphery of the straightener, which is to come into contact with a peripheral wall of the straightening passage, and the peripheral wall need precisely inclined relative to an axis of the straightening passage. Such axially inclined alignment of the outer periphery of the straightener is much more difficult compared with e.g. a parallel alignment of the same relative to the axis of the straightening passage, thereby resulting in a cost increase of the straightener. Also, in the case of the straightener as disclosed in the above-described Japanese utility model application published under SHOWA No. 39-17657, a straightener plate positioned along the axis of the straightening passage divides the straightening passage into a central passage portion and an outer periphery passage portion, the central passage portion has the same sectional area throughout its length, but the outer periphery passage portion disposed thereabout has its sectional area gradually reduced towards the downstream side, whereby the central passage portion and the outer periphery passage portion provide different straightening effects and manners of the fluid flow each other. Consequently, in this case also, the fluid straightening efficiency is low and it is impossible to prevent the generation of the vortex flow in the jetted fluid. However, if it is attempted to dispose the straightening plate with an inclination in order to equalize the straightening effects in the respective passage portions, there will occur considerable complication in the structure of the straightener and cost increase of the same.